System of telephonic communication



(No Model.) 2 Sheets-Sheet 1.

C. A. BELL.

SYSTEM OF TBLEPHONIG GOMMUNIOATION. No. 346,708. Patented Aug. 3, 1886.

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(No Model.) 2 Sheets-Sheet 2.

' G A. BELL.

SYSTEM OF TELEPHONIG COMMUNICATION. No. 346,708. Patented Aug. 3, 1886 QI U Wi-zin eaaetw. 7" Invenor .fl e/vcz/ 5 fiwm LII UNITE STATES PATENT@rrrca OHIOHESTER A. BELL, OF LONDON, COUNTY OF MIDDLESEX, ENGLAND.

SYSTEM OF TELEPHONIC COMMUNICATION.

SPECIFICATION forming part of Letters Patent No. 346,708, dated August3, 1886.

Application filed April 12, 1886. Serial No. 198,532.

To all whom it may concern.-

Be it known that I, CHIOHESTER A. BELL, residing at 128 Gower Street,London, \V." 0., in the county of Middlesex and Kingdom of England,haveinvented certain Improvements in Systems of TelephonicCommunication, of which the following is a specification.

This invention relates to the transmission of speech electricallybetween stations distant from one another by means of variableresistance-transmitting instruments actuated by a common voltaic batteryplaced at a central station.

My plan of operation differs materially from the arrangement ordinarilyemployed, and tends to economy in battery-power and simplicity inconstruction and manipulation. Heretofore each substation has beenprovided with a transmitting-telephone in which the current of a localbattery, varied in strength by the impact of the sound-waves produced bythe voice, acting through the medium of a vibratory plate on a variableresistance included in the circuit, is passed through the primary coilof an inductorium, the secondary coil thereof being connected in circuitwith and forming part of the line. The inductioncoil has been soemployed, as it has been considered impracticable to vary thecomparatively-high resistance of a line-circuit by the action of thevoice on a single transmitter sufficientl y to reproduce with accuracyarticulate sounds of the requisite strength or volume. The necessaryvariation of the current has therefore been effected in a short primarycircuit, and the induced currents thereby generated in the secondarycoil have been made the actual medium of communication. The employmentof the inductorium in this capacity has necessitated the use of abattery at every sub station. To obviate this necessity and to confinethe batteries to central stations, reducing materially their cost bygreatly diminishing the number of cells required, and at the same timeto retain the batteries which are actually in use under the care andsupervision of the attendants at the central station,

is the primary object of this invention.

It is quite evident that when each sub-station has a battery of its ownthe said battery is lying idle for a great portion of the time; but bymy invention the batteries may be in constant use, now in connectionwith one or more pairs or groups of circuits, and now with (No model.)

others; hence a small number of cells may take the place of a muchlarger number operated in the ordinary way. For the attainment of thisobject my invention comprises a novel arrangement of telephonic circuitsanda combination of the said circuits with a main bat-"6o tery andcertain resistances in such a way that a portion of the current of saidbattery may be varied by any individual transmitter, and the variationsso produced be propagated to a receiver connected'with any desiredsecond 6 line without interfering with any undesired line.

It further consists in combining the said circuit arrangements with aswitch-board or commntator for use in a telephone-exchange sys- 7o tem.

Myinvention contemplates a central station connected as usual with anydesired number of radial telephone-lines, each of which extends from thesaid central point to one or more sub-stations, where a variable mediumtransmitter and receiving-telephone are includedinthemaincircuit.Duringtheperiods of conversation between any two lines a voltaic batteryis connected in branch circuit to the pair of united lines, and thecurrent of the same pervading both lines, energizes both transmitters,and is itself varied in strength by the operation of either transmitter.

A suitable resistance is included in the battery '85 branch circuitbetween the point of union of the two lines and the battery, and thesame battery may be connected with a larger number ofpairs of unitedlines,the communications passing between the stations of each pair being0 totally exempt from interference due to the operation of the others,provided that a suitable resistance be included between each pair ofunited circuits and the battery branch. In such systems the transmitterpreferably has-a 5 comparatively high initial resistance.

I am aware that it has heretofore been proposed to centralizetransmitter-batteries, and that inventions tending to that end have beenpatented. As a due acknowledgment of the 10:) state of the art, I hererefer to the patents granted, respectively, to Charles E. Scribner, No.243,165, dated June 21, 1881, and to George Lee Anders, No. 252,986,dated January 31, 1882. The former case, however, re- 1(5 fers totransmitters provided with the usual induction-coil, while the lattercase describes exclusively a plan in which the central-office battery isincluded in direct circuit between the connected lines.

.For the better comprehension of my invention I will now describe thesame in detail, reference being made to the accompanying drawings, inwhich- Figures 1 and 2 are diagrams representing successive stepsillustrating the principle. Fig. 3 is a diagram showing a number ofcircuits connected in accordance with the terms of my invention; andFig. 4 is a diagram showing the application of the said invention to atelephone-exchange system.

The plan which I am about to describe for working any number oftelephonic circuits from a single battery in a central station isapplicable to all transmitters of high or comparatively high resistance,which operate by effecting considerable variation in that resistance,but more especially to such instruments as the jet-transmitter withplatinum electrodes and ajet of highly diluted sulphuric acid, describedin Letters Patent issued to me Februcry 16, 1886, and numbered 336,031.

Referring now to Fig. 1, B is a main battery of high electro-motiveforce, but of low internal resistance, one pole of which is grounded atG. From the other pole extends a main wire, d, to which twotelephone-lines, a and a, are respectively connected. Each of theselines connects at a distant station with a main line transmitter, D andE, and a receivingtele phone, Dand E, and the circuit of each line,after passing these instruments, connects with a ground-wire, 8. If twosuch transmitters, D and E, each provided, as shown, with thereceiving-telephone in the same circnit,D and E, be connected,as in Fig.1,on one side with earth direct and on the other through therespective'line-wires a and a to one pole of a battery, B, at a centralstation, the said battery being, as already indicated, of highelectro-motive force,but of low internal resistance,

- of the resistances of the lines a and a, and

even if the original vibrations be of so radical a nature as to beabsolutely a succession of makes and breaks of the circuit. This isreadily understood, if we consider that under these circumstanceschanges in the resistance of the transmitter cause disturbance in theelectric condition of the circuit, and that equilibrium is reestablishedthrough the battery and earth at the central station rather than throughthe second line and transmitter. In other words,the battery and earth atthe central station act as a shunt of resistance so small as to bepractically ignored.

Referring now to Fig. 2, it will be seen that the elements are identicalwith those of Fig. 1, with the following exceptions: that a resistance,R, is inserted between the point where the two lines a a meet and thepole of the battery. This, however, materially changes the conditions.The shunt at the central otfice is no longer one of no resistance, andthe electric disturbances originating in one transmitter (D for example)are propagated along the line b to the central station,are partlyexpended through the battery to earth, and partly along the line I)through the trans mitter E and to the telephone E, in which they becomeaudible. The extent of disturbance transmitted to E will depend on therelative resistances of R and of the line and instruments 1), E, E, s,and G, and it is very easy to make the resistance R so high thatpractically the whole of the electrical distnrbances created by theoperation of the transmitter D on the line!) are transmitted to E. Theinsertion of the resistance R naturally results in diminishing thetotality of current supplied to the lines I) and I) and the transmittersDand E; but this is readily com-- pensated for by increasing theelectro-motive force of the battery-a. 0., by increasing the number ofcells. The resistance R may be of any desired character-for example, a.short length of any material of inferior electrical conductivity, or arheostat comprising a coil or series of coils of any kind of fineinsulated wire. Iron wire is well suited for the purpose.

Although in Fig. 2 I-have shown but two lines brought into connection ata central station with the vitalizing-battery and resistance in branchcircuit, as described, it should be noted that I do not restrict myselfto that number. Three or more lines may be connected in a similar waywithout impairing the efliciency of the system; and I desire tobeunderstood throughout this specification that state ments madeapplying to a pair of lines will apply also to a greater number.

The amount of resistance R in short lines (such as ordinary city lines)may be varied within wide limits without appreciably affecting theaction of the transmitter D on the receiving-telephone E. Experimentshows that it may be 'varied from two thousand to eight thousand ohmswith the high-resistance jettransmitters described in the Patent No.336,081, hereinbefore cited, which offer a resistance of one thousandohms.

It is desirable in practice to make the resistance R adjustable in thesame manner as the well-known rheostat, as it may then be varied fromtime to time to compensate for hygrometrical variations.

Fig. 3 shows a number of pairs of substation lines connected with thesame main battery, B, each pair having a resistance, R, between thejunction of the two lines and the battery, precisely as in Fig. 2. Ihave, moreover, shown in Fig. 3 one group consisting of three lines, 01,d, and (1", connected with one another and with the same battery andresist ance R since the principle upon which this invention is based isequally applicable to groups of two, three, or more lines.

Referring to Fig. 3 it will be found that a second pair or group ofsub-station transmitting and receiving telephones, F F and H H,connected, as shown, through a second resistance, It, and lines 5 andb,will be in its operation totally free from interference with the linesandinstruments ofthe first pair orgroup, and that subscribers at D and Emay carry on a conversation together at the same time that F and H areconversing without either pair overhearing the other. Such is also thecase with respect to sub-stations at I and J K and L and M, and anynumber of others. Owing to the high resistance of each transmitter onlya very small quantity of electricity flows through it. Consequently withwellinsulated lines a very large number of pairs of transmitters may beworked from one battery of suitably low resistance. This particular planof working transmitters without induction-coils has other advantages. Ita pair of transmitters at outlying stations be connected through anindependent battery at the central station-that is, with the battery indirect circuit between the two linesthe electro-motive force or numberof cells of such battery must of necessity be double that of the singlebattery hereinbefore described. Furthermore, when so connected, if thetransmitters are of unequal resistance, the subscriber at thelowresistance end will not be so well heard as the subscriber at thehigh-resistance end. In practice I have found that two transmittersconnected, as hereinbefore described, with one pole of a battery work aswell as when a battery 0t double the electro-motive force is in directcircuit with both. I have also found that two transmitters havingelectrodes of different sizes,which do not work well when put in directcircuit with a bat-tery,work perfectly when joined to one pole of abattery through a very high resistance. Finally, in this system ahigh-resistance transmitter may be put in circuit either with anotherhigh-resistance transmitter or with the ordinary inductioninstrumcntswithout changing the battery.

Fig. 4 illustrates a plan of central station connecting devices arrangedfor practical operation in accordance with my invention.- Aswitch-board, S B, is placed at the central station, the form shownbeingthat of the well-- known universal switch or Swiss commutator,which is composed of vertical and horizontal bars, which, however, arenot in contactwith one another, except when metallic plugs are insertedin the holes at each point of intersection. It will be understood thatany other form of switch-board may be adopted without departing from thespirit of the invention.

The vertical bars N are connected with the respective line-wires 2, 3,4, 5, 6, and 7, and the horizontal bars 8, 9, and 10 are for the purposeof connecting any two or more lines together. Thetransverse orhorizontal bars are connected through separate resistances R, R and R",which are preferably adjustable, and by a wire, m, to the battery B.Each of the lines 2, 3, 4,850., proceed from the switchboard at thecentral stations, at each of which is placed a direct-circuittransmitter and a telephone-receiver, thelines being finally terminatedby ground-wires s at G. The vertical switch-board barsNeach constitutenormally open branches of the line circuits to which they are attached,and are only operative when their respective lines are connected forconversation. To serve as a suitable call-receiving arrangement, Iprovide, however. for the several main lines .normal central-officebranch terminals 3 4. 5, &c., each of which extends from a split-plugsocket, 6, (half of which is attached to the main and the other half tothe branch line,) through a correspondingly-numbered annunciator to acommon earth-plate. One vertical switchboard bar, I. is united to abranch wire, I, leading through the central-office transmitter t,receiver t, and,

ground-wire s to earth. Normally, when the lines are all at rest theplug connectors are all in place in the sockets e, and the main linesare thus continued at the central station through theannunciator-extensions to earth. For an ordinary tcle1;)hone-eXchangetheresistances, as hereinbet'ore stated. may be from two thousand ohmsupward, as circumstances may require. The battery must have largeplates, and an eleetro-motive force, of from thirty to forty volts,(about twenty mediumsized secondary cells will answer admirably.) Therequired electro-motive force will, however, depend on the resistance ofthe transmitter employed. Any kind of battery that does not run down orexhaust itself on open circuit maybe used, the essential condition beingthat the resistance thereof must be very low, not exceeding a few ohms.To talk from the central station with any sub-station it is onlynecessary to withdraw the plug p of the bar representing that stationfrom its normal socket c, to insert it in the hole at the intersectionof the same vertical bar with any one of the transverse bars, and toinsert the plug p of the vertical bar I, representing thecentral-station outfit at the intersection of the said bar I with thesame transverse bar. This is illustrated in the drawings, thesub-station line3 being connected with the ccntralol'fice telephones onthe middle transverse bar, 9. Conversation can thus be readilymaintained between the central station and any sub-station, and, if moreconvenient, an

ordinary induction-transmitter may be em ployed, as it is not essentialto the operation of the system that both transmitters shall be of thedirect-circuit type. To connect two or more sub-station lines, the plugsof the de sired lines are drawn from their respective normal sockets andinserted at the intersections of their respective vertical bars wit-hsome one of the transverse bars. The lines 2 and 6 are in the drawingsshown as 'being joined through the bar 8. The lines 4, 5, and

7 are shown as being at rest, their plug-connectors 1) being in theirnormal position. It

is, of course, obvious that instead of grounding one pole of thebattery, I may connect it by a return-wire with the distant terminal ofall the line-wires, and that my invention includes such an obviousmodification.

Having now described my invention and the way in which I operate thesame, I claim- 1. A system of telephonic transmission in which thetransmitters of the several lines are energized by a single battery, thesaid battery being located at a central point and connected in branch orderived circuit with any pair or series of pairs, sets, or groups oflines united for the purpose of telephonic intercommunication,wherebyinduction-coils and local batterries may be dispensed with, asdescribed.

2. A system of telephonic intercommunicalion in which the transmittersat sub-stations connected with line-wires centering at a common centralpoint, are energized byavoltaic battery located at the said centralpoint and connected in branch or derived circuit with any pair or groupor series of pairs or groups of lines, a resistance being interposedbetween each of the said pairs or groups of lines and the said battery,substantially as hereinbefore described.

3. In a system of telephonic transmission, the combination of a pair orgreater number of telephone main lines, telephone transmitters andreceivers included directly in the circuit of the said lines, and abattery connected in branch circuit with the said lines to energize thetransmitters, substantially as hereinbefore described.

4. The combination, substantially as hereinbefore described, ofa pair orgroup of telephonic main lines, variable-resistancetelephone-transmitters included in the circuit of each line, a batteryconnected in branch or derived circuit with the said lines, and aresistance interposedbetween the said battery and thejunction-point ofthe said main lines.

5. The combination of a telephone-circuit having three or more branches,each provided with a separate ground-terminal, two or more of whichbranches include direct-circu t transmitting and receiving telephones,and the remaining branch including a battery and resistance, the saidresistance being interposed between the battery and the junction-pointof the battery branch with the other two, substantially as hereinbeforedescribed.

6. In asystem of telephonic intercommunication, a series of sets oftelephone-lines, variable-resistance telephonic transmitters includeddirectly in circuit at the stations upon the said lines, areceiving-telephone also at each station, a battery at the centralstation having one pole connected with the earth, or with a return-wire,and having its other pole connected by branch circuits with each pair oflines, and a suitable resistance, as indicated, included between eachset of lines and the said battery, substantially as and for the purposesspecified.

7. In a system of telephonic circuits, one or more groups oftelephonicline-circuits, and telephonic transmitters and receiversincluded directly in the said line-circuits at the substations thereof,combined witha battery of lowinternal resistance but high electro-motiveforce located at a central station, one pole of which battery isgrounded and the other joined by branches to each of the said groups ofline-circuits, and a high resistance-such as an adjustable rheostat-foreach separate group of lines interposed between the said pairs and thebattery, whereby the said several groups are placed in communication,substantiallyas described.

8. Thecombination,inatelephone-exchange system, of a series oftelephone-lines radiating from a central station to a series ofsub-stations, a variable-resistance transmitter and areceiving-telephone included directly in the circuit of each of the saidlines, a battery at the central station with one of its poles'eoirnected to a ground or return wire, and having its other pole branched,as described, a rheostat or other suitable resistance included in eachof the said battery-branches, and switching devices, whereby any two ormore of the said circuit-lines may be connected to one another, and alsoto one of the said battery-branches, substantially as hereinspecified,and for the purposes set forth.

9. The combinatiomin a telephone-exchange system, of a series oftelephone-lines, each extending between one or more sub-stations and acentral station, a variableresistance transmitter adapted to be includeddirectly in the main circuit, (independently of an inductioncoil,) and areceiving-telephone at each substation, a series of earth-branches, eachincluding an annnnciator at the central station, one for each of thesaid lines, and normally united thereto, a central-stationbranch-eircnit including telephones, a battery at the central stationhaving one of its poles grounded and the other pole connected with aseries of normall y-open branches, a rheostat or other suitableresistance included in each of the said battery-branches, and means, asindicated, comprising a suitable switch-board and con necting-plugs, ortheir equivalents, whereby the several line-circuits may be transferredfrom their normal annunciator terminals and be connected in pairs orsets with one another, or with the central-station telephones, and alsowith one of the said battery-hranehes,whereby a single battery may beutilized for any num-v ber of direct-acting transmitters withoutinterl'erence, substantially as hereinbefore described.

In testimony whereof I have signed my name to this specification in thepresence of two subscribing witnesses.

OHICHESTER A. BELL.

\Vitnesses:

RIoHD. T. PLIMPTON, SAMUEL RIDEAL.

